Other than, What's the best lens to buy?, What camera to buy? is probably the most-asked photography question. There is no good answer. As a Canon user for 30 years, I believe in their products. I own three Canon cameras and am about to buy a fourth. One is a small deck-of-cards-sized P&S camera. It's superb for what it's designed to do. My DSLRs have served me very well for several years, for what they're designed to do.
The real question is, What do you want to do with your camera? If it's something you want for general all-around snapshot/vacation photography, the SX20 will more than do the job. The same can be said for just about all of Canon's point-and-shoot cameras. If you want to do serious photography this camera will also get the job done, if you understand that the inability to changes lenses will limit you. Note that I can show you several photographers who use cameras at this level and do superb "art" photography. But they have taken the time to learn the principles of photography and to understand what their cameras can and can't do. If you want it to photograph your corals/fish, it will also get the job done, but there will be limits in terms of the types of shots you can get.
When buying a camera of any kind, the most important thing, after determining whether it has the features you want and you can afford it, is to hold the camera. Is it comfortable to hold? Do the controls make sense to you and can you use them? If you have small hands, a camera that is too big and heavy will always feel like you're picking up a brick and you won't use it as much. If you have big hands, a camera that is too small will be difficult to operate and you'll feel like you're always hitting three buttons when you want just one. Again, you'll be less inclined to use it. Find a camera that feels good in your hands, isn't too light or heavy, and that you feel you can control.
That's the best answer I can give to the open-ended "What camera should I buy?" question, which is essentially what you're asking. If you have specific plans for your photography, state those and I'll be able to better help you.
Is the SX20 a good camera? Most likely, yes. Will it capture quality images? Yes. Will it capture high-quality images? Within its limitations and depending on how much effort you put into the photography.
Gary
